After appearing in "Operation Mad Ball" (1957), Hickey would not return to features for a decade until he took small roles in "The Producers" (1967) and "The Boston Strangler" (1968). Stage work kept him busy; over the years Hickey has appeared on and off-Broadway in plays including "Tovarich", "On the Town", "Thieves", "Happy Birthday Wanda June", "Troilus and Cressida" and "Next". He was also part of the American Shakespeare Festival Theater for six years in the 60s. His acting students, meanwhile, included the likes of James Woods, Judd Hirsch, Billy Crystal, Carol Kane, Christine Lahti, Tom Berenger and Amy Wright.
Feature work picked up slightly for Hickey in the 70s, and, though some of the films were obscure, they included such intriguing items as "A New Leaf" (1971) and John Huston's "Wise Blood" (1979). Huston remembered the diminutive and feisty actor when he was casting the key supporting role of an elderly, amusing but still deadly Mafia Don in "Prizzi's Honor" (1985); Hickey's splendid turn in the role won him an Oscar nomination as Best Supporting Actor and kicked off a highly prolific period in film that has lasted for over a decade. He has played a variety of patriarchal and avuncular figures since then, often crotchety, occasionally villainous and sometimes quite funny, in a wide range of films including "The Name of the Rose" (1986), "Da" (1988), "Sea of Love" (1989), "My Blue Heaven" (1990) and "Major Payne" (1995). Hickey also enjoyed himself immensely supplying the voice of the evil scientist for the animated hit, "Tim Burton's The Nightmare Before Christmas" (1993).
More recent stage work for Hickey included the Broadway revival of "Arsenic and Old Lace" (1986-87), with Hickey as the deadly Jonathan Brewster's ferrety sidekick Dr. Einstein. TV credits, meanwhile, have included TV-movies including "Stranded" (1986) and "Mob Boss" (1991). Hickey also tried a series with the ABC sitcom "Baby Boom" (1991-92), and got laughs with a recurring role as the obnoxious, babbling Carlton on the hit sitcom "Wings".